Orthicons, also known as orthicon tubes, are a type of cathode-ray tube (CRT) used in early television cameras and image sensor devices. The term "orthicon" originates from the Greek words "ortho," meaning straight or correct, and "icon," referring to an image or representation.
Orthicons function by converting light signals into electrical signals. The tube consists of several layers designed to capture and amplify images projected onto its surface. The outer layer, known as the target or photocathode, is a photosensitive material that reacts to light by emitting electrons. Inside the tube, there is an accelerating electrode and a focusing electrode, which help focus and accelerate the electron beam.
The core component of orthicons is the impact layer, located behind the photocathode, which contains a multitude of light-sensitive granules. When the electron beam hits the impact layer, the granules release secondary electrons, causing an electrical current proportional to the light intensity.
Orthicons allowed for the conversion of optical images into electrical signals, which could be further processed and transmitted as television signals. They played a crucial role in the early days of television broadcasting, enabling the live capture and transmission of moving images. As technology advanced, orthicons were gradually replaced by more efficient imaging devices, such as vidicons and charge-coupled devices (CCDs), which offered higher resolution and decreased size.
Today, orthicons are mostly considered outdated technology, with their usage limited to certain niche applications or as historical artifacts in the study of television history and image sensors.
